This invention relates to vehicle dehumidifying mechanisms in general, and specifically to such a system with an improved thermal and air flow efficiency.
U.S. Pat. No. 5,509,275 issued Apr. 23, 1996 to Bhatti, et al., and co-assigned to the assignee of the subject invention, discloses a system for continually dehumidifying ambient air that is drawn into a heating, ventilating and air conditioning (HVAC) system of a motor vehicle. Typically, hot air which is also quite humid is simply pulled directly in and forced over a cold evaporator core, which cools the air as well as condensing water out of the air. While drier air enters the passenger cabin, relying upon condensation by the evaporator core brings its own problems, especially microbial growth and its attendant odor. The patent noted provides a desiccant wheel of novel design that continually turns, at slow speed, within the HVAC housing, removing moisture in desiccant lined tubes in an adsorption half of the wheel, which are regenerated in a heated half of the wheel through which hot air is forced. The two xe2x80x9chalvesxe2x80x9d of the wheel are defined by stationary rubbing seals. The tubes run axially from face to face of the wheel, but are not tightly packed, leaving space between for a radial cross flow of outside air that is blown over the outside of the tubes, in both halves of the wheel. The radial cross flow cools the tubes in the adsorption half of the wheel, removing the latent heat released by the desiccant when it adsorbs moisture. The cooling of the tubes in the adsorption half of the wheel is beneficial, since the heat released by the working desiccant is thereby prevented from reaching the evaporator core.
However, the same cross flow, when it crosses the other half of the wheel, is cooler than the heated air simultaneously passing through the inside of the tubes to regenerate the desiccant. Therefore, the cross flow air can potentially reduce the efficiency of the concurrent regeneration process as it passes through the other half of the wheel. In addition, much of the limited volume of the wheel is the empty space necessarily left between the tubes. Since space is at a premium in any HVAC housing, more complete utilization of the volume within the wheel would be desirable.
The subject invention discloses a more space efficient desiccant wheel that provides maximum utilization of the space within the wheel, combined with a novel system of ducts and seals that confines the radial cross cooling flow only to that half of the wheel where it is most beneficial.
In the preferred embodiment disclosed, the entire internal volume of the wheel, defined between a pair of axially spaced, annular end faces and a concentric outer cylindrical wall and central inner tunnel, is occupied by a closely packed array of evenly circumferentially spaced cells. Each cell is comprised of a pair of solid conductive metal leaves, separated by a constant thickness in a spiral pattern radiating from the central tunnel to the outer wall. A first set of cells, including every other cell contains a constant thickness, corrugated conductive metal fin, with axially oriented corrugations that run the entire axial length of the cell, from end face to end face. The cells in the first set are also axially open at each end face, but radially blocked throughout, because of the orientation of the fin corrugations. Therefore, in the first set of cells there is a potential axial flow path through, but not radial. A second set of cells, including those cells intermediate the first set, contains similar fins, with the same thickness and orientation, but with the axial end of each fin cut off at an angle to provide diagonally and radially opposed openings through the outer wall and central inner tunnel. Each cell of the second set of cells is deliberately blocked at both annular end faces, however. Therefore, in the second set of cells, there is a potential radial flow path from outer wall to inner tunnel (a compound radial and axial flow path), but no axial flow path from end face to end face. The fins in the first set of cells are desiccant coated, while those in the second set of cells are not, and all fins are tightly engaged with the leaves separating the individual cells, so as to provide efficient heat conductive paths through the adjacent cells that are otherwise sealed from one another in terms of potential air flow. In effect, all possible space within the wheel is taken up by cell spaces and their contained fins.
Within the HVAC system and housing, a novel system of ducts and seals directs various air flows through selected cells with maximum thermal efficiency, taking best advantage of the improved space efficiency of the wheel itself. Stationary rubbing seals against the faces of the wheel divide the wheel space enveloped into two basic halves that are also stationary, an adsorption half and a regeneration half, as with the previously patented design noted above. As the wheel slowly turns, cells from each set of cells turn through each half of the space successively and repeatedly. Humid outside air is directed through an outside air feed duct at a front end face of the wheel within the adsorption half of the divided space envelope. Since cells in the second set are axially blocked, humid air flows axially through only cells in the first set, passing axially over their desiccant coated fins. Moisture is adsorbed, and the latent heat released is conducted by the same fins across shared leaves and into adjacent cells in the second set.
Concurrently, outside air (or air at a similar ambient temperature) is fed radially through a feed manifold to the outer wall of the wheel, within the adsorption half of the envelope, and radially enters only cells from the second set (since cells in the first set are radially blocked). The cross flow of air flows radially through and axially across the fins of those cells of the second set of cells located within the adsorption half of the envelope, removing the released heat of adsorption conducted from adjacent cells. Because of the design of the wheel, all available volume within the adsorption half of the envelope is occupied either by cells involved in moisture adsorption, or cells involved in heat removal, with no dead or wasted space. Cross flow air in the adsorption half of the envelope eventually exits its cells into the central tunnel, which is axially blocked by a cap at the front end face. A semi-cylindrical, stationary rubbing seal blocks those radial openings in the central tunnel located in the regeneration half of the envelope. The capped tunnel and the semi-cylindrical seal together create a radial cross flow exhaust duct that directs the cross flow axially out and away from the wheel at the back face, preventing it from radially entering those cells of the second set located in the regeneration half of the envelope.
Also, concurrently, externally heated air is directed through a regeneration duct to the back end face of the wheel on the regeneration half of the space envelope, flowing axially only through those cells of the first set located in the regeneration half (since, again, cells of the second set are axially blocked). The heated air dries and regenerates the desiccant in the cells of the first set, without being cooled by any cross flow air in adjacent cells of the second set, improving the efficiency of operation. Regeneration air with moisture driven out of the desiccant is then axially exhausted away from the front face of the wheel. In addition, in the embodiment disclosed, the radial cross flow air that is exhausted from the central tunnel at the back face of the envelope tunnel is captured and used as pre heated entry air for the regeneration duct and its heater, so that the removed heat of adsorption is not wasted.